C++ test fails intermittently

```
When building the C++ module and running the accompanying test, I get different
results between invocations. About 50% of the time the test completes
successfully. The rest of the times, I get this error:

diff_bisect: Timeout. FAIL
Expected: (Diff(DELETE,"cat"), Diff(INSERT,"map"))
Actual: (Diff(DELETE,"c"), Diff(INSERT,"m"), Diff(EQUAL,"a"), Diff(DELETE,"t"),
Diff(INSERT,"p"))
Test failed: diff_bisect: Timeout.
Total time: 6 ms
Done.

I see this both with the 20111117 release and trunk.

```

Original issue reported on code.google.com by `kstuts...@gmail.com` on 25 Dec 2011 at 7:20